It is well known that, in a simulated moving-bed type chromatographic separator, a plurality of unit packed columns (hereinafter, also referred to as simply “packed column”), each packed with an adsorbent exhibiting a selective adsorbability for a specified component among two or more components contained in a feed solution, are connected in series, and an endless circulation system is formed by connecting a most downstream-side unit packed column to a most upstream-side unit packed column to form a packed bed as a whole, and the feed solution and eluent are supplied to the packed bed, a fraction (fraction A) high in moving speed in the packed bed and a fraction (fraction C) low in moving speed in the packed bed are extracted, respectively, from positions different from each other, and the position for supply of the feed solution, the position for supply of the eluent, the position for extraction of the fraction A and the position for extraction of the fraction C are moved in order toward the downstream side in the fluid circulation direction in the packed bed while being maintained at a constant positional relationship, thereby simulatively realizing an operation of a moving bed capable of performing a continuous supply of feed solution (for example, Patent document 1).
In such a simulated moving-bed type chromatographic separator, because the liquid is circulated in the packed bed while the supply of the feed solution and the eluent and the extraction of fractions A and C are always carried out, usually, at least a feed solution supply pump, an eluent supply pump and one or more circulation pump are required. In particular, because the circulation pump is fixed between certain unit packed columns, the discharge amount thereof varies periodically accompanied with the supply of the feed solution, the supply of the eluent or the extraction of the respective fractions. Further, because the concentration and the composition of the fluid flowing into the circulation pump vary in order, accompanying therewith, the properties such as specific gravity and viscosity of the fluid vary. As a difference between the set value of the flow rate of the circulation pump and the actual flow rate of the actual fluid becomes greater, the separation ability decreases. Therefore, an expensive control device is required in order to automatically control the flow rate of the circulation pump in accordance with such an alteration of the flow rate set value or a variation of the properties.
Further, as an operation method which is not a general simulated moving-bed type chromatographic separation wherein a liquid is circulated in a packed bed while supply of feed solution and eluent and extraction of fractions A and C are always carried out, many operation methods are proposed, such as those disclosed in Patent documents 2 and 3. In an operation method disclosed in Patent document 2, although the control is simple and a high separation performance can be obtained, because the concentration and the composition of the fluid flowing into the circulation pump also vary, accompanying therewith the properties such as specific gravity and viscosity of the fluid also vary. Further, since the circulation pump is periodically repeated in operation/stop, the pressure variation in the system becomes great, and in order to avoid this, an operation such as delaying the timing of shutting off the inside of the packed bed becomes necessary, and whereby, the control becomes complicated.    Patent document 1: Japanese Patent 2,962,589    Patent document 2: JP-A-2001-334103    Patent document 3: JP-B-60-55162